Studies completed, underway or planned include investigations on the: a) nephrotoxicity and potential antitumor activity of reactive GSH conjugates [e.g., S-2-chloroethyl GSH; diglutathionyl bromohydroquinone and S-(1,1,2,3,4-pentachloro 1:3-butadienyl)-GSH]; b) role of hepatic metabolism in the formation and subsequent transport of these conjugates to the kidney; c) Gamma-glutamyl cycle and mercapturic acid biosynthetic pathway in normal renal and in Gamma-GT positive tumor cells. Initial emphasis has been primarily on determining whether chloroethylnitrosoureas (i.e., MeCCNU, chlorozotocin) manifest their nephrotoxicity via the formation of reactive GSH conjugates (i.e., S-2-chloroethyl GSH). Preliminary data have shown that pretreatment with inhibitors of Gamma-glutamyltranspeptidase activity protected against MeCCNU nephrotoxicity in vivo. Pretreatment with an inhibitor of GSH synthesis (BSO) resulted in a marked decrease in liver and kidney GSH, and to a corresponding increase in covalent binding by chloroethyl labeled MeCCNU in liver. However, covalent binding to kidney protein or DNA was decreased by nearly 50%. An unidentified metabolite of MeCCNU has been isolated from the bile of MeCCNU treated rats. This metabolite was found to be toxic to a tumor cell line possessing high GammaGT activity. In vitro studies utilizing rat liver microsomes have demonstrated the formation of chloroethyl-derived GSH conjugates of MeCCNU which were formed by an NADPH dependent reaction. These studies provide preliminary evidence which suggests that MeCCNU is metabolized to a GSH conjugate which may produce nephrotoxicity and possess antitumor activity.